In a plasma display panel (hereinafter referred to as PDP or panel), gas discharge generates ultraviolet rays, and the ultraviolet rays excite phosphor to illuminate for color display. The PDP has a structure provided with display cells divided by barrier ribs on a substrate, and a phosphor layer is formed in each display cell.
PDP can be divided broadly into an AC type and a DC type when classified by their driving methods, and there are two kinds of discharge methods, a surface discharge type and an opposed discharge type. However, in view of high definition, large screen and easiness of manufacturing, the mainstream of the PDP is now those of the surface discharge type with a 3 electrode structure. The AC type surface discharge PDP has such a structure that comprises pairs of adjoining display electrodes formed in parallel to each other on a substrate, address electrodes arranged in a direction traversing the display electrodes, barrier ribs and phosphor layers formed on another substrate. This structure is suitable for color display using phosphor material because it allows formation of a comparatively thick layer of the phosphor.
Plasma display devices using such PDP have many advantages including their capabilities of high-speed display, wider viewing angle, adaptability for upsizing, higher display quality because of the self-luminous function, and the like, as compared to liquid crystal display panels. These features thus gain attention especially in recent years among various kinds of flat-panel display devices, and many PDP are used for a variety of purposes such as displays in public places where many people gather, and displays in private homes for family members to enjoy images in large screens.
Description is now provided of a structure of PDP with reference to FIG. 8. FIG. 8 is a perspective view showing a structure of PDP. As shown in FIG. 8, a plurality of rows of display electrodes 2, each comprising a pair of scan electrode and sustain electrode are formed in a striped pattern on transparent substrate 1 made of a glass plate or the like on the front side, dielectric layer 3 is formed in a manner to cover a group of these electrodes, and protective film 4 is formed over dielectric layer 3.
On the other hand, there are a plurality of rows of address electrodes 7 of a striped pattern formed on substrate 5 on the back side in a direction of traversing display electrodes 2 consisting of the scan electrodes and the sustain electrodes on substrate 1 at the front side confronting substrate 5, and the rows of address electrodes 7 are covered with insulation layer 6. A plurality of barrier ribs 8 are provided on the surface of insulation layer 6, each arranged in a space between adjoining address electrodes 7 in parallel thereto, and side surfaces of barrier ribs 8 and the surface of insulation layer 6 are covered with phosphor layer 9.
Substrate 1 and substrate 5 are arranged face to face with a small discharge space between them in a manner that display electrodes 2 consisting of the scan electrodes and the sustain electrodes and address electrodes 7 cross at generally right angles to one another, and their peripheries are hermetically sealed. The discharge space is charged with discharge gas such as a mixture of neon and xenon gases, for example. Furthermore, the discharge space is divided by barrier ribs 8 into a plurality of compartments forming the plurality of discharge cells, each containing a crossing point between display electrode 2 and address electrode 7. Phosphor layers 9 for producing red, green and blue colors are disposed one after another in a sequential order into the individual discharge cells.
FIG. 9 is a wiring diagram showing an arrangement of the electrodes of the PDP. As shown in FIG. 9, combinations of the scan electrodes and the sustain electrodes, and the address electrodes configure a matrix structure of “M” rows by “N” columns, in which “M” number of scan electrodes SCN1 through SCNM and sustain electrodes SUS1 through SUSM are arranged in the direction of rows, and “N” number of address electrodes D1 through DN are arranged in the direction of columns.
In the PDP of such an electrode configuration, a write pulse applied between one of the address electrodes and one of the scan electrodes generates an address discharge between the address electrode and the scan electrode in selected one of the discharge cells. After that, cyclic sustaining pulses, the polarity of which reverses alternately, are impressed between the scan electrode and the sustain electrode to maintain the discharge between the scan electrode 20: and the sustain electrode, and to provide a given display.
FIG. 10 is an exploded perspective view showing a structure of a plasma display unit assembled with a PDP. In FIG. 10, an enclosure for housing PDP 10 consists of front frame 11 and metal back cover 12. Front frame 11 has an opening in which front cover 13 made of a glass plate or the like is provided to protect PDP 10, in addition to the function as an optical filter. Front cover 13 has a coating of vapor-deposited silver, for instance, to suppress undesired emission of electromagnetic waves. Besides, back cover 12 is provided with a plurality of vent openings 12a for dissipating heat generated by PDP 10 and the like.
PDP 10 is secured by bonding to a front surface of chassis base 14 constructed of aluminum or the like via heat conductive sheet 15, and a plurality of circuit blocks 16 for driving PDP 10 are mounted to the backside of chassis base 14.
Heat conductive sheet 15 effectively conducts and dissipates the heat generated by PDP 10 to chassis base 14 in order to allow PDP 10 and electric circuits mounted on circuit blocks 16 for display driving to operate steadily. An air-cooling fan may also be mounted to chassis base 14 at the same side where circuit blocks 16 are mounted, when necessary, to exhaust the heat transferred to chassis base 14.
Circuit blocks 16 carry electric circuits to perform display drive and control of PDP 10, and the electric circuits are connected electrically to lead-conductors of the electrode tapped out around the side edges of PDP 10 with a plurality of flexible wiring sheets (not show in the figure) that extend over the four side edges of chassis base 14. In addition, chassis base 14 is provided with bosses 14a, which are integrally formed by die-casting or the like method in a manner to protrude from the back surface of chassis base 14, for mounting circuit block 16 and for securing back cover 12. Alternatively, chassis base 14 may be constructed with a flat aluminum plate and cylindrical pins fixed to it.
An AC type PDP such as the one described above is constructed generally of two main parts, a front panel and a back panel, and it is manufactured in the following manner.
First, an electrode of transparent conductive film is formed on a surface of a front side glass substrate. Bus electrodes are formed thereafter by printing and firing an electrode material such as silver (Ag) to provide display electrodes. A dielectric layer is formed over these display electrodes by coating and firing a dielectric glass material. Afterwards, a protective film of magnesium oxide (MgO) is formed by such a method as vapor deposition, to complete the front panel.
On the other hand, address electrodes are formed by printing and firing an electrode material such as silver (Ag) on a surface of a back side glass substrate, and an insulation layer is formed by coating and firing a glass material. Furthermore, barrier ribs are formed into such configuration that separates the address electrodes, and phosphor layer is then formed by coating and firing phosphor materials between the barrier ribs, to complete the back panel.
After the front panel and the back panel have undergone the prescribed processes respectively, sealing glass frit is coated around the back panel, and it is put together with the front panel. The front and the back panels are then subjected to a sealing process which heats and melts the glass frit to seal together their peripheral edges. This assembly is then put into a vacuuming process to discharge the air inside a discharge space formed between the front and the back panels, while the assembly is being heated, and the inner discharge space is filled thereafter with discharge gas to a predetermined pressure. This completes manufacturing of the PDP.
An electrical discharge characteristic of the PDP manufactured through the process described above changes substantially with time. It is for this reason that the PDP is subjected to an aging process to produce electrical discharge by application of a prescribed voltage for a predetermined time period, to stabilize the discharge characteristic, as disclosed in Japanese Patent Unexamined Publications 1999-213891 and 2002-75207.
There have been such problems, however, that glass substrates composing the front panel and back panel crack while being subjected to the aging process for the characteristic stabilization, which eventually cause damages to the glass substrates.
Generally, most of electronic components used for electrical products are subjected to aging process for stabilization of their characteristics. Since one of objects of the aging process is to break down defective portions produced in the manufacturing process of the electronic components so as not to permit any defective product to go out, in addition to the characteristic stabilization, such cracks in the PDP during the aging process had not been considered to be a significant problem. However, there is now an upward demand for improvement of productivity of the PDP since the plasma display devices are put into the limelight as large-size displays, and the demand continues to increase.
The present invention addresses the problems described above, and it aims at preventing the panels from being cracked in the aging process.